Two-way telephone system



April 1s, 1933. E. R. TAYLOR 1,904,567 Two-WAY TELEPHONE SYSTEM FiledJune 16, 1931 INVENTOR ATTORNEY Patented pr. 18h, 1933 UNITED STATESPATENT OFFICE EDMUN D R. TAYLOR, 0F NEW YORK, N. Y., AVSSIGNOR TOAMERICAN TELEPHONE AND TELEGRAPH COMPANY, CORPORATION OF NEW YORKTwo-WAY TELEPTONE 'SYSTEM Application filed June 16,

This invention relates to two-way transmission systems, and moreparticularly to two-way transmission systems having a return loss at oneend which is very high and a return loss at the other end which is lowenough to permit appreciable reflection o f transmitted waves. l

`While the invention is applicable to many types of two-way transmissionsystems, itV is especially applicable to radio telephonesystems fortwo-way communication between aircraft and the ground and to similarsystems for ship-t-o-shore communication.

The prinicpal object of the invention is the suppression of echoes andsinging in the two-way system. A further object is to accomplish suchsuppression without the requirement of a comparatively elaborate set ofapparatus for the purpose.

The invention will be understood when the following description of onedesirable embodiment is read with reference to the accompanying'drawing. Figure l of the drawing shows diagrammatically, and in partschematically, a two-way system such as a ship-toshore radio telephonesystem, while Fig. 2 shows in like manner the circuits at one of thestations in a slightly modilied arrangement. Like reference char--acters in the two figures of the drawing designate correspondingelements.

YVith reference to the details of Fig. l, there is shown a system fortwo-way telephone communication between a station l at the left and astation 2 at the right. Transmission from left to right takes place overthe one-way path LLl of station l and the one-way path LL2 of station 2,which are interconnected by a radio link.- Similarly, transmission fromright to left takes place over the path LLl of station 2, theintermediate radio link and the path LL2 of station l. t station thefour-wire circuit formed bythe two one-way vpaths just described may beextended to the left over the two-wire circuit L, to which the four-wirecircuit is connected through ahybrid coil HC. The usual network Nbalances the two-wire line L. At station 2 the path LLZ- leads to a,Vtelephone receiver, whilethe path 19311 seriai- No. 544,890. v

LLl leads from a telephone transmitter. From this description it will beunderstood that the two-way system shown is one which` has a return lossat station 2 which is very high and a return loss at station 1 which maybe quite low so as to cause an appreciable reflection over path LL1 ofwaves transmitted in path LL2.

In connection with transmission from left to right, waves pass through avolume control device and a radio transmitter T and are radi-ated fromthe antenna A1 at station l to the antenna A2 at station 2. They thenpass through the radio receiver R and on to the telephone receiver. Thewaves from the telephone transmitter at station 2 pass through a volumecontrol device and the radio transmitter T and Amay be radiated from theantenna A1 to the antenna A2 at the distant station l. At that station apath is provided through a one-way amplifier and the radio receiver R,and the waves may then be transmitted on to the hybrid coil HC and thetwo-wire circuit L.

In connection with the applicants arrangements for transmission controlto suppress echoes and singing, it should be noted that the transmittingpath LL1 at station l and the receiving path LL2 at station 2 arenormal-ly in operative condition, whereas the transmitting path LLl ofstation 2 and the receiving path LL2 of station l are normally disabledat the points e and b, respectively.

lAssociated with the radio transmitter T at station l is .an oscillatorwhich applies to the left-right channel continuously carrier waves of afrequency f1. When the signals are ap-v plied to the system fortransmission inthis direction they are modulated upon the carrier f1 andthus transmitted to station 2.

In connection with transmission from station 2 to station l,thereisspecic'ally disclosed an oscillator' which impresses upon the iradio transmitter T a frequency f2. As specifically disclosed orindicated, this frequency f2 represents the carrier waves which maybeemployed for the transmission of the voice signals after modulation fromstation 2 to station l. It is to be understood, however, that thisfrequency f2 might, for the purposes of the invention, as well be someother control frequency than a carrier frequency employed formodulation. At station l it will be noted that a filter F, passingsubstan- 5 tially only the frequency f2, and a detector D are connectedacross the path LL2 at the point L in the output of the one-wayamplifier, and that the output circuit of the de,- tector D includes thewindings of relays R1 and R2.

' in the radio transmitter T upon the carrier f1 from the oscillatorshown, and radiation takes place from antenna A1 to antenna A2. Atstation 2 demodulatien takes place in the radio receiver R', and thewaves representing the voice pass over path LL2 to the telephonereceiver.

Vhen the speaker at station 2 talks into the telephone transmitter, thevoice waves pass over the path LLl and through the volume controldevice. As indicated above, the oscillator which generates the frequencyf2 is connected to the radio transmitter T, but the path LLl is normallydisabled at the point c. A portion of the voice energy is diverted fromthe path LLl at point Z and operates the amplifier-detector AD. Therelays R1 and R2', the windings of which vare includedvin the output ofthe amplifierdetector, now operate. The operation of relay R1 removesthe disability from the transmitting path LLI at point e and permits theradiation from the antenna A1 of the car- 'rler f2 upon which the voicehas been modulated. Thus, the normal disability at point e is removed inresponse to the voice energy sent over the path LLL to permit transmis-'sion to station l. Theoperation of relay R2 disables the receiving pathLL2 at point g.

This disability serves to suppress false transmission in LL2 due toradio coupling between antenna A1 and antenna A2', for instance Atstation l the waves transmitted from the distant antenna A1 are pickedup in the antenna A2 and are passed through the oneway amplifier. Thereceiving path LL2 is Vnormally disabled at the point in order toprevent false transmission of static or other interfering energy whichmight be picked up by the antenna A2. At point a, a portion of thetransmitted energy is diverted, and the .carrier or control energy offrequency f2 passes the filter F, the voice frequencies heingsubstantially excluded. Thus, the detector D operates substantially onlyin respense to energy of the frequency f2. Wlhen the relays R1 (and R2)operate in response to the operation of the detector, the path LL2 iscleared of the disability at point l), and the voice waves are free topass on to the hybrid coil HC. The operation of relay R2 places adisability upon the transmitting path LL,L at point c; thus, any wavesreflected back over this path as echoes of the waves in path LL2 aresuppressed and prevented from reaching the radio transmitter.

It is repeated here and should be carefully noted, that the control ofrelays R1 and R2 at station 1 may be effected by any control frequencysent from station 2, which control frequency may or may not be thecarrier intermittently applied at station 2 for the transmission of thevoice waves. Withreference to Fig. 2 of the drawing, there is shown asomewhat modilied arrangement of the circuits of station 2. It will benoted that the transmitting path LL1 is normally disabled, and that theremoval of the disability is effected by relay R1', as in the case ofFig. l; likewise, it will be noted that the receiving path LL2 may bedisabled by the operation of relay R2 as is the casein Fig. 1. Theserelays, however, are controlled in the arrangement of Fig. 2 not by aportion of the voice energy diverted from path LL2 but by the manualoperation of a switch S, which is connected in series with the windingsof relays R1 and R2 and a battery B. This switch may take the form of apush button which an operator operates at the proper time to open up thetransmitting chanel LLl and to permit the radiation of the voice and thecarrier or other control energy.

It will be seen, after an examination of the description containedhereinabove, that the applicants arrangement has the advantage that linenoise from circuits connected to the four-wire circuit over the line Lat station l ceases to be a factor in the problem of controllingtransmission over the paths LL1 and LL2. Accordingly, the duties of anopx erator at this point are materially reduced.

More specifically, the relays at station l can-c not be affected by linenoise to produce false operation of the transmission controls. It willbe noted further that the degree of unbalance of the circuits connectedto the hybrid coil HC becomes immaterial since the transmission controlrelays are rendered quite immune to false operation. The only remainingpossibility of false' operation at station l is connected with radionoise or static picked up .by the antenna A2. ASince the filter F isdesigned to pass substantially only the special frequency f2, thispossibility of false operation becomes negligible. At station 2 it is,Vof course, possible for noise currents to reach the amplifier-detectorAD, but in a system such as that disclosed and such as those to" whichthe invention is especially applicable, the transmitting connection LLlis quite short and there is little likelihood of noise energy ofappreciable level being found in the path LLl.

While the invention has been disclosed somewhat specifically for thepurpose of illustration, it is to be understood that it is capable ofembodiment in many other and Widely different forms Within the scope ofthe appended claims.

lVhat is claimed is:

1. In a two-Way system for the transmission of energy, a first pathadapted for transmission in one direction and a second path adapted fortransmission in the opposite direction, each of said paths comprisingtwo terminal sections and an intermediate transmission link, theterminal sections of said second path being normally disabled, meansnear the transmitting end of said first path for applying carrier energycontinuously thereto, means near the transmitting end of said secondpath for removing the disability :from the transmitting section thereofand applying control energy thereto, and means responsive substantiallyonly to said control energy for removing the disability from thereceiving section of said second path and disabling the transmittingsection of said first path.

2. In a two-Way system for the transmission of energy, a first pathadapted for transmission in one direction and a second path adapted fortransmission in the opposite direction, each of said paths comprisingtwo terminal sections and an intermediate transmission link, theterminal sections of said second path being normally disabled, meansnear the transmitting end of said first path for applying carrier energycontinuously thereto, means near the transmitting end of said secondpath for disabling the receiving section of said first path, removingthe disability from the transmitting section of said second path andapplying control energy to said second path, and means responsivesubstantially only to said control energy for removing the disabilityfrom the receiving section of said second path and disabling thetransmitting section of said first path.

3. In a system for the transmission of energy, a first path adapted fortransmission from a first to a second station and a second path adaptedfor transmission from the second station to the first, the return lossat the first station being comparatively loW and the return loss at thesecond station being comparatively high, each of said paths comprisingtwo terminal sections and an intermediate link, means normally appliedto each terminal section of said second path for disabling the same,means near the transmitting end of said second path for removing thedisability from the transmitting section thereof and applying controlenergy thereto, and means responsive substantially only to said controlenergy for removing the disability from -the. receiving section ofv'said second path and disabling the transmitting section of saidlirstpath. y

4. In a system for"the'transmissionot en'- ergy, a first path adaptedfor' transmission from a first station to a second station fand a secondpath adapted fortransmissionfrom the second station to the first, thereturn loss at the first station being comparativelyilow and the returnloss at the second station being comparatively high, each of said pathscomprising two terminal sections and an intermediate link, meansnormally applied t'o the receiving section of said second path for dis-labling the same, means associated With said first path for effectingtransmission over the intermediate link thereof lby continuously appliedcarrier energy, means associated with vsaid second path for effectingtransmis-A sion over the intermediate link thereof by carrier 'energyapplied intermittently under the control of the energy transmitted toproduce the desired overall effect, and means responsive substantiallyonly to said intermittently applied carrierenergy'for removingpthedisability from the receiving'section" of saidv second path anddisabling the transmitting section of said first path. Y v

5. In a telephone system, tvvo distant stations separated by anintermediate link. .a two-Way extending circuit terminating. at thefirst station, a transmitting connection and a receiving connectionadapted for one-Way transmission from and to said two-Way circuit,respectively, at said first station, a telephone receiver and atelephone transmitter at the second station,.a receiving pathfortransmission to said receiver and a transmitting path fortransmission from said transmitter at said second station, saidtransmitting path and said receiving connection being normally disabled,means at'said second station for removing the disability fromsaidtransmitting path, applying control yenergy thereto and disablingsaid receiving path, and means at said first station responsivesubstantially only to saidcontrol energy `for removing the disabilityfrom said receiving'connection and disabling said transmittingconnection.

6. In a telephone system, tWo distant stations separated'byV anintermediate link,I a two-Way extending circuit terminating at the firststation, a transmitting connection and a receiving connection adaptedfor one-Way transmission from and to said two-Way circuit, respectively,at said first station, a telephone receiver and a ltelephone transmitterat the secondy station, a receiving path for' transmission tol saidreceiver and a transmit-` ting path for transmission from saidtransmitter at said second station, said transmitting path and saidreceiving connection being normally disabled, `means associated Withsaid transmitting connection for applying carrier energy continuouslythereto for trans- IOO mission from said y'first to said secondstations, means at said' second' station respon-` sive to voice wavesfrom said transmitter for disabling said receiving path, removing thedisability from said transmitting path and applying carrier energythereto, and means at said first station responsive substantially onlyto the.carrier energy applied at said second station for removing thedisability from said receiving connection and disabling saidtransmitting connection.-

7. In a two-way telephone system including a two-wire circuit, a firstone-way path adapted for transmission from said two-wire circuit to adistant telephone receiver and a second one-way path adapted fortransmission from the telephone transmitter associated with saidreceiver to said two-wire circuit, each of said one-way paths comprisingtwo end sections and an intermediate link, the method of renderingthesystem independent of interfering energy which consists in normallymaintaining the two end sections of said second one-way path in disabledcondition, removing the disability from the transmitting section of saidsecond one-way path and applying control energy thereto when voice wavestravel therein, and causing'said control energy upon reaching the otherend of said second one-way path to remove the disability from thereceivingsection thereof and to disable the transmitting section of saidfirst one-way path. Y

8. In a two-way telephone system including a two-wire circuit, a firstone-way path adapted for transmission from said two-wire circuit to adistant telephone receiver and a second one-way path adapted forftransmission from the telephone transmitter associated with saidreceiver to said two-wire circuit, each of said one-way Vpathscomprising two end sections and an intermediate link, the method ofrendering the system independent of interfering energywhich consists innormally maintaining the two end sections of said second one-way path indisabled condition, causing the voice waves traveling inV thetransmitting section of* said second one-way path to remove thedisability therefrom, to apply carrier waves thereto and to` disable thereceiving section of said lirst one-way path, and causing said carrierwaves upon reaching the other end of said second one-way path to removethe disability from the receiving section thereof and vto disable thetransmitting section of said first one-'way path.

In testimony whereof, I have signed my name to this specification this13th day of June 1931.

EDMUND R. TAYLOR.

